GRQ #4 - Synaptic Activity

Question 1

Signals are transmitted between neurons at locations called

Answer 1

synapses

Question 2

what is a synapse?

Answer 2

it is where a neuron meets its target cell

Question 3

synapses that occur between two neurons are called

Answer 3

neuronal synapses

Question 4

neuronal synapses can be of 2 types. They are:

Answer 4

electrical and chemical

Question 5

What is an axodendritic synapse?

Answer 5

a synapse that occurs between an axon and a dendrite

Question 6

what is an axosomatic synapse?

Answer 6

a synapse that occurs between an axon and a cell body

Question 7

what is an axoaxonic synapse?

Answer 7

a synapse that occurs between an axon and another axon

Question 8

What are the two terms used to describe the neurons sending and receiving messages?

Answer 8

Presynaptic and postsynaptic neurons

Question 9

what is a presynaptic neuron

Answer 9

it is the neuron that is sending the message from its axon terminal

Question 10

what is a postsynaptic neuron

Answer 10

it is the neuron that is receiving the message from its dendrite, cell body or axon

Question 11

what is a synaptic transmission

Answer 11

it is the transfer of chemical and electrical signals between neurons at a synapse

Question 12

___ is the fundamental process for most functions of the nervous system

Answer 12

synaptic transmission

Question 13

Each neuron has an ___ number of synapses

Answer 13

enormous

Question 14

An axon generally splits into over __ axon terminals

Answer 14

1,000

Question 15

Each axon terminal meets up with another

Answer 15

axon, dendrite or cell body

Question 16

on average, a presynaptic neuron generally forms synapses with about how many postsynaptic neurons?

Answer 16

about 1,000

Question 17

A post synaptic neuron can receive input from as many as ____ presynaptic neurons

Answer 17

10,000

Question 18

what is an electrical synapse

Answer 18

they occur between cells that are electrically coupled via gap junctions

Question 19

how do gap junctions function

Answer 19

gap junctions are between two axolemmas of two neurons that are nearly touching and the junctions contain precisely aligned channels that form pores through which ions and other small substances can travel

Question 20

Gap junctions allow the __

Answer 20

electric current to flow directly from the axoplasma of one neuron to axoplasma of another neuron

Question 21

do the axolemmas of the neurons touch at an electrical synapse?

Answer 21

No - they are separated by about 3.5 nanometers (so they are nearly touching)

Question 22

what are two unique features of electrical synapses

Answer 22

1. synaptic transmission is bidirectional

2. synaptic transmission is nearly instantaneous

Question 23

what do electrical synapses’ unique features allow for

Answer 23

they allow the activity of a group of cells to be synchronized; when stimulated, the cells will produce action potentials in unison

Question 24

explain synaptic transmission being bidirectional in electrical synapses

Answer 24

it means that either neuron in an electrical synapse may act as the presynaptic or the postsynaptic neuron and thus the electrical current may flow in either direction between the two cells

Question 25

explain synaptic transmission being nearly instantaneous in electrical synapses

Answer 25

the delay between depolarization of the presynaptic neuron and change in potential of the postsynaptic neuron is less than 0.1 miliseconds which is crazy fast

Question 26

where are electrical synapses found in the nervous system?

Answer 26

primarily in areas of the brain that are responsible for programmed, automatic behaviors like breathing; also present in developing nervous tissue in the embryo and fetus and are thought to assist in the development of the brain

Question 27

where are electrical synapses found outside the nervous system?

Answer 27

they can be found in cardiac and visceral smooth muscle where they allow those tissues to engage in coordinated muscle activity

Question 28

the vast majority of synapses in the nervous system are __. why?

Answer 28

chemical synapses because they are more efficient.

Question 29

what is a chemical synapse

Answer 29

a type of synapse in which a presynaptic neuron releases neurotransmitters to trigger a change in a postsynaptic neuron

Question 30

what happens to the electrical current in an electrical synapse?

Answer 30

they eventually become weaker as the current dissipated into the extracellular fluid

Question 31

do chemical synapses lose strength/weaken?

Answer 31

no - chemical synapses convert an electrical signal into a controlled chemical signal so no strength is lost

Question 32

where is the chemical signal reconverted back into an electrical signal?

Answer 32

in the postsynaptic neuron

Question 33

what are the 3 structural differences between a chemical and electrical synapse

Answer 33

1. synaptic vesicles
2. synaptic cleft
3. neurotransmitter receptors

Question 34

explain the role of the synaptic vesicles

Answer 34

this is how the electrical signal of the action potential is converted into a chemical signal ; every chemical synapse houses synaptic vesicles in the axon terminal of the presynaptic neuron. the vesicles contain chemical messengers called neurotransmitters that transmit signals from the presynaptic to postsynaptic neuron

Question 35

explain the role of the synaptic cleft

Answer 35

the cells of a chemical synapse are separated by a microscopic gap between the axon terminal of a presynaptic neuron and its target cell called the synaptic cleft. it is filled with extracellular fluid and proteins like enzymes; 20-50 nm (slightly larger than the gap junctions in electrical synapses)

Question 36

explain the role of neurotransmitter receptors

Answer 36

the postsynaptic neuron must have receptors to which the neurotransmitters released by the presynaptic neuron can bind or it cannot respond to the signal being transmitted; receptors are generally linked directly or indirectly to ion channels

Question 37

how is the chemical signal converted back into an electrical signal in a chemical synapse

Answer 37

through the ion channels that the neurotransmitter receptors are linked to

Question 38

what causes chemical synapses to transmit signals more slowly than electrical synapses

Answer 38

the three unique structural differences

Question 39

what is the synaptic delay

Answer 39

the short delay between the arrival of the action potential at the axon terminal of a presynaptic neuron and the postsynaptic potential of a postsynaptic neuron

Question 40

how long is the synaptic delay

Answer 40

0.5 millisecond gap between the arrival of the action potential at the axon terminal and the effects on the postsynaptic neuron’s membrane

Question 41

because chemical synapses are ____ the message can only be sent by the presynaptic neuron

Answer 41

unidirectional

Question 42

what is allowed by the 3 structural differences of the chemical synapse that is not permitted by the structure of the electrical synapse

Answer 42

the signal can vary in size - this means that if more neurotransmitters are released then the presynaptic neuron has a greater effect on the postsynaptic neuron

Question 43

the signal in an electrical synapse will always be __

Answer 43

the same size

Question 44

the effect that the presynaptic neuron triggers can vary with different

Answer 44

neurotransmitters and receptors

Question 45

what is step 1 (the first thing that takes place) at a neuronal synapse

Answer 45

an action potential in the presynaptic neuron triggers calcium ion channels in the axon terminal to open - an action potential reaches the axon terminal of the presynaptic neuron, which triggers the opening of voltage-gates calcium ion channels in its axolemma

Question 46

what is step 2 at a neuronal synapse

Answer 46

an influx of calcium ions causes synaptic vesicles to release neurotransmitters into the synaptic cleft - these calcium ions enter the axon terminal causing synaptic vesicles in the area to fuse with the presynaptic membrane and this releases neurotransmitters into the synaptic cleft via exocytosis

Question 47

what is step 3 at a neuronal synapse

Answer 47

neurotransmitters bind to receptors on the postsynaptic neuron - the neurotransmitters diffuse across the synaptic cleft where they bind to neurotransmitter receptors on the membrane of the postsynaptic neuron

Question 48

what is step 4 at a neuronal synapse

Answer 48

ion channels open, leading to a local potential and possibly an action potential : the binding of neurotransmitters to receptors generally either opens or closes ligand-gated ion channels in the postsynaptic membrane resulting in a local potential (this local potential may or may not lead to an action potential in the postsynaptic neuron)